Faced with the worst summer fire season in 10 years, Gov. Jerry Brown is proposing broad new changes to California’s logging rules that would allow landowners to cut larger trees and build temporary roads without obtaining a permit as a way to thin more forests across the state.

The proposal — which has the support of the timber industry but is being opposed by more than a dozen environmental groups — would represent one of the most significant changes to the state’s timber harvesting rules in the past 45 years.

The legislative session ends for the year next Friday. On Thursday, the details were still being negotiated by legislative leaders and the governor’s office behind the scenes and had not yet been formally introduced in a bill or put up for a vote. “They are trying to get to some kind of a deal,” said Rich Gordon, the president of the California Forestry Association, a timber industry group. “They are looking at what can get done politically.”

Under Brown’s proposal, private landowners would be able to cut trees up to 36 inches in diameter — up from the current 26 inches — on property of 300 acres or less without getting a timber harvest permit from the state, as long as their purpose was to thin forests to reduce fire risk. They also would be able to build roads of up to 600 feet long without getting a permit, as long as they repaired and replanted them.

Timber industry officials say the changes are needed to cut red tape and increase incentives for landowners, particularly in the Sierra Nevada, to thin pine and fir forests that have become dangerously overgrown after 100 years of fire fighting.